Given two non-empty binary trees s and t, check whether tree t has

exactly the same structure and node values with a subtree of s.

A subtree of s is a tree consists of a node in s and all of this node's descendants.

The tree s could also be considered as a subtree of itself.

Example 1:

Given tree s:

3    / \   4   5  / \ 1   2

Given tree t:

4   / \ 1   2

Return true, because t has the same structure and node values with a subtree of s.

 

Example 2:

Given tree s:

3    / \   4   5  / \ 1   2    /   0

Given tree t:

4  / \ 1   2

Return false.

思路：

首先定义一个函数，用来判断两颗二叉树是否相等。然后判断一颗二叉树t是否是二叉树s的子树，

仅需依次递归判断二叉树s的左子树和右子树是否与t相等即可。

 

bool isSameTree(TreeNode* s, TreeNode* t){    if(s == NULL &&  t== NULL) return true;    if( (s == NULL && t != NULL )|| (s != NULL&&t == NULL) || (s->val !=t->val)) return false;    bool left = isSameTree(s->left,t->left);    bool right = isSameTree(s->right,t->right);    return (left && right);}bool isSubtree(TreeNode* s, TreeNode* t){    bool res = false;    if(s!=NULL && t!= NULL)    {        if(t->val== s->val)      res = isSameTree(s,t);        if(!res) res = isSubtree(s->left,t);        if(!res) res = isSubtree(s->right,t);    }    return res;}